Many well and expansion tanks use a diaphragm or bladder to separate air from water. An air charge pressure on one side keeps the diaphragm/bladder at a distance away from the inside wall of the tank in the air dome. When the tank is installed onto a water system, the water system pressure pushes back against the diaphragm/bladder, compressing the air. The proper pre-charge will continue to keep the diaphragm/bladder away from the tank wall. If the pre-charge pressure is not enough to provide an air volume appropriate for the water supply pressure, the diaphragm/bladder will fill the air cell. If eventually the diaphragm/bladder “bottoms out” on the tank wall, the tank becomes ineffective in the function it has been design to provide. Various failure modes for well/expansion tanks include a low air pre-charge, bladder failure resulting in leak of air charge, and installation of an undersized tank causing the diaphragm/bladder to overwork, all of which can lead to quick cycling and ultimately failure.